It is the long-range goal of this project to study the co-oxygenation of chemicals, i.e., benzo(a)pyrene (BP) 7,8-diol during the metabolism of arachidonic acid (AA) by guinea pig lung, ram seminal vesicle, mouse skin, microsomes, and cells grown in tissue culture. BP-7,8-diol was oxidized to 7,10/8.9 tetrol by prostaglandin synthetase by all the tissues examined. Electrophilic metabolites of BP-7,8 diol were formed since BP-7,8 diol was covalently bound to protein. Significance of this metabolic activation in relation to cell transformation is being examined.